1. Field of the Invention
The present invention relates generally to diodes formed within integrated circuits. More particularly, the present invention relates to high current carrying capacity polysilicon diodes formed within integrated circuits.
2. Description of the Related Art
Integrated circuits are formed from semiconductor substrates within and upon whose surfaces are formed resistors, transistors, capacitors and other electrical circuit elements. The electrical circuit elements are connected internally and externally to the semiconductor substrate upon which they are formed through patterned conductor layers which are separated by dielectric layers.
In addition to forming resistors, transistors and capacitors within integrated circuits, it is common in the art of integrated circuit fabrication to also employ diodes within integrated circuits. Diodes formed within integrated circuits may serve any of several functions, including but not limited to current rectification functions and electrostatic discharge protection functions.
While the use of diodes within integrated circuits has become quite common in the art of integrated circuit fabrication, the fabrication of diodes, and in particular junction diodes, within integrated circuits is not entirely without problems. In particular, as integrated circuit device densities continue to increase and integrated circuit device dimensions continue to decrease, it has become increasingly difficult to form through conventional structures and methods within advanced integrated circuits junction diodes which meet the needs, and in particular the current density requirement needs, of advanced integrated circuits.
Conventionally, junction diodes within complementary metal oxide semiconductor (CMOS) integrated circuits and bipolar complementary metal oxide semiconductor (BiCMOS) integrated circuits have been formed within monocrystalline silicon substrates within and upon which are formed those integrated circuits. Unfortunately, such a conventional junction diode may often not easily be operated in a forward bias mode since one of the junction diode electrodes is typically not available for biasing. In addition, such a conventional diode when properly biased may also often induce a parasitic effect, such as but not limited to parasitic latch-up effect with an adjoining junction transistor formed within the monocrystalline silicon substrate within which is formed the conventional junction diode, thus causing malfunction of the integrated circuit within which is formed the junction transistor. While the use of a lateral (ie: horizontal) polysilicon junction diode formed from a single polysilicon layer separated from a monocrystalline silicon substrate by a dielectric layer provides a junction diode construction not susceptible to either a forward biasing limitation or a parasitic effect, such a lateral polysilicon junction diode in general typically has a limited cross-sectional junction area (ie: typically less than about 5 square microns) and thus a relatively low current carrying capacity, unless fabricated with an exceedingly large projected surface area (ie: greater than about 200 square microns) upon the dielectric layer.
Diodes, in general, and polysilicon junction diodes, in particular, with relatively high current carrying capacity are typically desirable within integrated circuits which are employed to control or dissipate relatively high levels of electrical power. In that regard, polysilicon junction diodes with a relatively high current carrying capacity within advanced integrated circuits typically desirably have a junction area of greater than about 20 square microns (excluding any pertinent metal contact areas) through which is carried a current of about 8 to about 10 milliamps, in order to provide a junction diode current density of no greater than about 2.6E4 to about 3.3E4 amps per square centimeter. It is thus towards the goal of forming within integrated circuits junction diodes with relatively high current carrying capacity that the present invention is generally directed.
Various types of diode constructions for use within integrated circuits have been disclosed in the art of integrated circuit fabrication. For example, Tsuzuki et al., in U.S. Pat. No. 4,760,434 discloses a lateral planar junction diode construction formed upon an insulator layer within a control circuit of an integrated circuit, where the integrated circuit has both the control circuit and a power circuit surrounding the control circuit. The lateral planar junction diode construction serves as a heat sensing element within the control circuit employed to control the power circuit, thus avoiding overheating of the power circuit. In addition, Takeshita et al., in U.S. Pat. No. 4,920,513 disclose a junction diode formed within a semiconductor substrate adjoining a capacitor formed within and upon the semiconductor substrate. The junction diode and the capacitor provide a pair of active elements within a dynamic random access memory (DRAM) memory cell of reduced dimension formed within and upon the semiconductor substrate.
Further, Rao et al., in U.S. Pat. No. 5,355,014 discloses an integrated circuit device which comprises an integrated resistor and capacitor formed within a semiconductor substrate, along with a schottky diode formed within and upon the semiconductor substrate. The integrated circuit device is useful in filtering electromagnetic interference (EMI) and radio frequency interference (RFI) produced by high speed data lines in digital computers and computer peripherals. Finally, Buerger, Jr., in U.S. Pat. No. 5,471,087 discloses a semi-monolithic integrated circuit memory cell comprising a capacitor formed over a semiconductor substrate and two junction diodes formed within the semiconductor substrate. One of the two junction diodes is employed in charging the capacitor, while the other of the two junction diodes is employed in discharging the capacitor.
Desirable in the art are additional junction diode constructions which may be employed within integrated circuit fabrications. More desirable in the art are additional junction diode constructions which may be employed within integrated circuit fabrications which require junction diodes of comparatively high current carrying capacity, while simultaneously providing junction diode constructions not susceptible to parasitic effects, such as but not limited to parasitic latch-up effects, with other electrical circuit elements within the integrated circuits within which are formed the junction diode constructions, thus compromising operation of the integrated circuits within which are formed the junction diode constructions. Particularly desirable in the art are additional junction diode constructions which fulfill the foregoing criteria, where the junction diode constructions may readily be fabricated through conventional integrated circuit fabrication schemes and methods to provide junction diodes which may be biased in either a forward mode or a reverse mode. It is towards the foregoing goals that the present invention is more specifically directed.